Abstract 5034: The antitumor immune response generated by radiation therapy may be limited by tumor cell adaptive resistance and can be circumvented by PD-L1 blockade

Radiation therapy and immunotherapy: what is the optimal timing or sequencing?

Radiotherapy is a component of the standard of care for many patients with locally advanced nonmetastatic tumors and increasingly those with oligometastatic tumors. Despite encouraging advances in local control and progression-free and overall survival outcomes, continued manifestation of tumor progression or recurrence leaves room for improvement in therapeutic efficacy. Novel combinations of radiation with immunotherapy have shown promise in improving outcomes and reducing recurrences by overcoming tumor immune tolerance and evasion mechanisms via boosting the immune system's ability to recognize and eradicate tumor cells. In this review, we discuss preclinical and early clinical evidence that radiotherapy and immunotherapy can improve treatment outcomes for locally advanced and metastatic tumors, elucidate underlying molecular mechanisms and address strategies to optimize timing and sequencing of combination therapy for maximal synergy.

Phase Ib/II trial evaluating the safety, tolerability and immunological activity of durvalumab (MEDI4736) (anti-PD-L1) plus tremelimumab (anti-CTLA-4) combined with FOLFOX in patients with metastatic colorectal cancer

BACKGROUND

5-Fluorouracil plus irinotecan or oxaliplatin alone or in association with target therapy are standard first-line therapy for metastatic colorectal cancer (mCRC). Checkpoint inhibitors targeting PD-1/PD-L1 demonstrated efficacy on mCRC with microsatellite instability but remain ineffective alone in microsatellite stable tumour. 5-Fluorouracil and oxaliplatin were known to present immunogenic properties. Durvalumab (D) is a human monoclonal antibody (mAb) that inhibits binding of programmed cell death ligand 1 (PD-L1) to its receptor. Tremelimumab (T) is a mAb directed against the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4). This study is designed to evaluate whether the addition of PD-L1 and CTLA-4 inhibition to oxaliplatin, fluorouracil and leucovorin (FOLFOX) increases treatment efficacy.

METHODS

This phase II study (ClinicalTrials.gov NCT03202758) will assess the efficacy and safety of FOLFOX/D/T association in patients with mCRC (n=48). Good performance status patients (Eastern Cooperative Oncology Group <2) with untreated, RAS mutational status mCRC will be eligible. Prior adjuvant therapy is allowed provided recurrence is >6 months postcompletion. There is a safety lead in nine patients receiving FOLFOX/D/T. Assuming no safety concerns the study will go on to include 39 additional patients. Patients will receive folinic acid (400 mg/m²)/5-fluorouracil (400 mg/m² as bolus followed by 2400 mg/m2 as a 46-hour infusion)/oxaliplatin (85 mg/m2) every 14 days with D (750 mg) D1 every 14 days and T (75 mg) D1 every 28 days. After six cycles of FOLFOX only D/T will continue until disease progression, death, intolerable toxicity, or patient/investigator decision to stop. Primary endpoint is safety and efficacy according to progression-free survival (PFS); secondary endpoints include overall response rate and quality of life. Hypothesis is that a PFS of 50% at 6 months is insufficient and a PFS of 70.7% is expected (with α=10%, β=10%). Blood, plasma and tumour tissue will be collected and assessed for potential prognostic and predictive biomarkers.